Many reports have appeared on the attempted specific targeting of tumor cells with monoclonal antibody-drug conjugates (Sela et al, in Immuno-conjugates, 189-216 (C. Vogel, ed. 1987); Ghose et al, in Targeted Drugs 1-22 (E. Goldberg, ed. 1983); Diener et al, in Antibody mediated delivery systems, 1-23 (J. Rodwell, ed. 1988); Pietersz et al, in Antibody mediated delivery systems, 25-53 (J. Rodwell, ed. 1988); Bumol et al, in Antibody mediated delivery systems, 55-79 (J. Rodwell, ed. 1988); G. A. Pietersz & K. Krauer, 2, J. Drug Targeting, 183-215 (1994); R. V. J. Chari, 31 Adv. Drug Delivery Revs., 89-104 (1998); W. A. Blattler & R. V. J. Chari, in Anticancer Agents, Frontiers in Cancer Chemotherapy, 317-338, ACS Symposium Series 796; Ojima et al eds, American Chemical Society 2001; J. M. Lambert, 5 Current Opinion in Pharmacology, 543-549 (2005); P. R. Hamann, 15 Expert Opinion on Therapeutics Patents, 1087-1103 (2005)). All references and patents cited herein are incorporated by reference.
Cytotoxic drugs such as methotrexate, daunorubicin, doxorubicin, vincristine, vinblastine, melphalan, mitomycin C, and chlorambucil have been conjugated to a variety of murine monoclonal antibodies. In some cases, the drug molecules were linked to the antibody molecules through an intermediary carrier molecule such as serum albumin (Garnett et al, 46, Cancer Res. 2407-2412 (1986); Ohkawa et al 23, Cancer Immunol. Immunother. 81-86 (1986); Endo et al, 47 Cancer Res. 1076-1080 (1980), dextran (Hurwitz et al, 2 Appl. Biochem. 25-35 (1980); Manabi et al, 34 Biochem. Pharmacol. 289-291 (1985); Dillman et al, 46 Cancer Res., 4886-4891 (1986); Shoval et al, 85, Proc. Natl. Acad. Sci., 8276-8280 (1988)), or polyglutamic acid (Tsukada et al, 73, J. Natl. Canc. Inst., 721-729 (1984); Kato et al, 27 J. Med. Chem., 1602-1607 (1984); Tsukada et al, 52, Br. J. Cancer, 111-116 (1985)).
A wide array of linker technologies has been employed for the preparation of such immunoconjugates and both cleavable and non-cleavable linkers have been investigated. In most cases, the high cytotoxic potential of the drugs could only be observed, however, if the drug molecules could be released from the conjugates in unmodified form at the target site using a cleavable linker.
In vitro cytotoxicity tests, however, have revealed that antibody-drug conjugates could kill not only antigen-positive cells, but also other cells in the vicinity, irrespective of the antigen expression on their surface. This phenomenon is called the bystander effect. This effect was observed in conjugates of the anti-CanAg antibody, huC242, with maytansinoids and with a CC1065 analog (Erickson et al, 66 Cancer Res., 4426-4433 (2006); Kovtun et al, 66 Cancer Res., 3214-3221 (2006)). So far only conjugates linked via a cleavable bond such as reducible disulfide bond demonstrated bystander cytotoxicity, while conjugates linked via a non-reducible thioether link exhibited no bystander effect.
Highly potent cytotoxic effector molecules linked to targeting agents such as antibodies could generate potent drug derivatives after intra-cellular processing of the conjugate. This could be an issue if generated cellular metabolites display undesired or not easily manageable side effects. In order to control the toxicity of antibody-drug conjugates, it could be very beneficial to use non-cleavable linkers.
Another major drawback with most antibody-drug conjugates is their inability to deliver a sufficient concentration of drug to the target site because of the limited number of targeted antigens and the relatively moderate cytotoxicity of cancerostatic drugs like methotrexate, daunorubicin, and vincristine. In order to achieve significant cytotoxicity, linkage of a large number of drug molecules, either directly to the antibody or through a polymeric carrier molecule, becomes necessary. However, such heavily modified antibodies often display impaired binding to the target antigen and fast in vivo clearance from the blood stream. So an alternative is to use much more potent drug molecules such as the ones disclosed herebelow.
Non cleavable linkers have been also used in conjugation. They have an interest in radioimmunotherapeutic applications in particular. This has been also utilized in the attachment of toxins to monoclonal antibodies, as for Pseudomonas exotoxin with MAb 9.2.27 using heterobifunctional maleimide succinimidyl 4-(N-maleimidomethyl)cyclohexane-1-carboxylate (SMCC) (EP 306943). The MAb toxin conjugate turned out to be of greater specificity in vitro against positive cell lines than the corresponding disulfide bond conjugate and thus less toxic in mouse models. Nonspecific toxicity is significantly decreased when a noncleavable linker is used. This non-cleavable linker has been used in the case of trastuzumab (Herceptin) which target HER2 (ErbB) HERR2 is a key target and methods are being investigated to maximize the effect of using MAbs to inhibit this receptor. One approach aims to augment the efficacy of trastuzumab (Herceptin) by coupling it to a chemotherapeutic agent, thus enabling the delivery of cytotoxic therapy at a cellular level (Ranson and Sliwkowski, 63 (Suppl. 1) Oncology, 17-24 (2002)).
Other versions of the SMCC reagent exist, for instance water soluble sulfosuccinimidyl 4-(N-maleimidomethyl)cyclohexane-1-carboxylate (sulfo-SMCC), has been also used in conjugation reaction. Other non-cleavable linkers include in particular N-succinimidyl-S-acetylthioacetae (SATA), SATA-SMCC, 2-iminothiazole (2IT) and 2IT-SMCC (Foulon et al, 10, Bioconjugate Chem., 867-876 (1999)). Crosslinking reagents comprising a haloacetyl-based moiety have also been used and include N-succinimidyl-4-(iodoacetyl)-aminobenzoate (SIAB), N-succinimidyl iodoacetate (SIA), N-succinimidyl bromoacetate (SBA) and N-succinimidyl 3-(bromo-acetamido)propionate (SBAP). These crosslinking reagents form non-cleavable linkers derived from haloacetyl-based moieties.
In spite of the above-reported difficulties because of the drug molecules, useful cytotoxic agents comprising cell binding moieties and the group of cytotoxic drugs known as maytansinoids have been reported (U.S. Pat. No. 5,208,020, U.S. Pat. No. 5,416,064, and R. V. J. Chari, 31 Advanced Drug Delivery Reviews 89-104 (1998)). Similarly, useful cytotoxic agents comprising cell binding moieties and analogues and derivatives of the potent antitumor antibotic CC-1065 have also been reported (U.S. Pat. No. 5,475,092, U.S. Pat. No. 5,585,499 and U.S. Pat. No. 6,756,397).
Tomaymycin derivatives are pyrrolo[1,4]benzodiazepines (PBDs), a known class of compounds exerting their biological properties by covalently binding to the N2 of guanine in the minor groove of DNA. PBDs include a number of minor groove binders such as anthramycin, neothramycin and DC-81. Tomaymycin antitumor activity is however limited because of its non-specific toxicity towards normal cells. Thus there is a need to increase the therapeutic activity, and diminish the non-specific toxic effects of tomaymycin compounds. The present inventors have shown that this need can be met by targeted delivery of tomaymcin compounds by linking them to cell binding agents. Additionally, there is a need to develop tomaymycin derivatives that are soluble and stable in aqueous solutions. Further, tomaymycin is not sufficiently potent to be used in conjugates of cell binding agents.
Recently, a few new PBD derivatives and their anti-tumour activity in preclinical models have been disclosed (WO 00/12508 and WO 2005/085260). However, initial clinical trials in humans indicate that compounds of this class are severely toxic, based on the very low dose that can be administered to humans (I. Puzanov, Proc. AACR-NCI-EORTC International Conference, Philadelphia, USA 2005, Abstract #B117). Thus, it is desired to provide alternative derivatives showing lesser side effects without compromising the cytotoxic activity.
International applications WO 2007/085930 and WO 2008/010101 describe tomaymicin derivatives that can be linked to a cell binding agent through a linker, but the linker is not a linker as defined for the compounds of the invention.
Article “Tetrahedron Letters, Vol. 29, N°40, pp. 5105-5108” describes tomaymicin derivatives ref. (13)-(15) without any linker.
International application WO 2005/085250 describes dimers of PBDs of general formula PBD-A-Y—X-(Het)na-L-(Het)nb-L-(Het)nc-T-(Het′)nd-L-(Het′)ne-L-(Het′)nf-X′—Y′-A′-PBD′ wherein Het and Het′ are amino-heteroarylene-groups of formulae -J-G-J′ or J′-G-J- where G is an optionally substituted heteroarylene, na-nf are integers between 0 and 5, L can be β-alanine, glycine, 4-aminobutanoic acid or a single bond. X and X′ are both either —NH— or —C(═O)— and Y and Y′ are divalent groups such that HY is an alkyl, heterocyclyc or aryl group or a single bond. A and A′ are selected from O, S, NH or a single bond. T is a divalent linker of the form —NH-Q-NH— or —C(═O)-Q-C(═O)— where Q is divalent group such that QH is an alkyl, heterocyclyc or aryl group (optionally substituted). The compounds according to the general formula all comprise —NH— or —C(═O)— as X and X′ and —NH-Q-NH— or —C(═O)-Q-C(═O)— which is not the case for the compounds of the invention.
International application WO 2005/023814 describes dimers of PBDs protected on the nitrogen atom N10 by R10—COO— comprising a bridge —X—R″—X— wherein R″ is an alkylene group optionally interrupted by one or more heteroatoms NH, O or S and/or aromatic rings and X is O, S or NH. There is no mention of a linker on the bridge —X—R″—X—. Moreover, the compounds of the invention are not protected on N10.
Article “European Journal of Medicinal Chemistry Vol. 40, N°7, pp. 641-654” describes dimers of PBDs ref. (38)-(40) that do not comprise any linker as for the compounds of the invention.
Article “Expert opinion; Monoclonal antibody-drug conjugates”, Ashley publications, Vol. 15, N°9, 2005, pp. 1087-1103, ISSN:1354-3774 does not describe the compounds of the invention and article “Cancer Res. 2006, 66(8), pp. 4426-4433” describes maytansinoid linked to cell binding agents.